Next issue with my Worcester Bosch and Hive

[Ab12]

Ok a few of you will know my last few posts of swapping out a 3 port valve for 2 X 2 ports, and wiring in hive for CH and stats for UFH.

All controls fine, valves open, boiler fires... and so becomes my next problem

The boiler, set at 5 on the HW dial, gets a call for heat. Heats up, gets to 75* and then stops heating (the active heating light) goes off on the boiler (hive is still feeding a switched live at this point - all good there). Boiler temp drops to 41* and then it fires back up, in the same cycle. Nothing shows up on the display, no fault, no overheat nothing.

most recently the gas valve and damaged board had been changed, so don't think they are the culprit...

 

[Ab12]

Established it might be the pump sticking. Freed but it stuck back up again. Is it a simple job of changing pump head or does the whole assembly need to come out.

Question is really, does the pump head have the pump impeller on it or does that remain in the boiler and may still stick